The present invention relates to a water-in-oil type silicone emulsion composition, more particularly to a water-in-oil type silicone emulsion composition having excellent stability to temperature changes, high safety against the skin and excellent texture when applied to the skin.
Silicone fluids and gumlike siloxane high polymers, so-called silicone gums, are characterized in that they are physiologically highly safe, hardly deteriorate and have excellent water repellency, and cosmetics containing such high polymers, when applied to the skin or the like, spread well, are less tacky and impart oil-free and smooth touch and gloss to the skin, so that they are widely employed cosmetic ingredients. Meanwhile, cyclic dimethylsiloxane oligomers are employed as ingredients for antiperspirants and the like because of their excellent compatibility with silicone fluids and hydrocarbon cosmetic ingredients, excellent spreadability and absence of chilliness when they volatilize.
There are disclosed a number of techniques for obtaining stable oil-in-water type emulsions of polyorganosiloxanes by means of emulsion polymerization using ordinary surfactants as emulsifiers or in the presence of specific emulsifiers. However, water-in-oil type emulsion compositions of polyorganosiloxanes are not yet successful in exhibiting satisfactory stability to temperature changes.
As a method for obtaining water-in-oil type emulsion compositions of polyorganosiloxanes, there is known a technique of employing various kinds of lipophilic polyorganosiloxane-polyoxyalkylene block copolymers as emulsifiers. It should be noted here that the block copolymers referred to herein mean those each having a linear polyorganosiloxane as the main chain and polyoxyalkylene chains at the terminal ends and/or as side chains and include so-called graft copolymers having polyoxyalkylene chains as side chains only.
For example, Japanese Provisional Patent Publication Nos. 66752/1986, 212321/1986, 212324/1986, 218509/1986, 45656/1987 and 54759/1987 disclose water-in-oil type emulsion compositions of polyorganosiloxanes prepared by using block copolymers of various structures as emulsifiers and by adding organically modified clay minerals. In Examples of these official gazettes, there are employed as such polyorganosiloxanes containing polyoxyalkylene chains at each terminal end and as side chains those having relativity low viscosity values of 60 to 200 cSt at 25xc2x0 C. While it is reported that these compositions are stable at temperatures of 0 to 50xc2x0 C. and are also stable to a temperature cycle between 5 and 45xc2x0 C., they failed to show sufficient stability to temperature cycles including cooling to a low temperature of xe2x88x9210xc2x0 C.
Japanese Provisional Patent Publication No. 215510/1987 discloses water-in-oil type emulsion compositions of polyorganosiloxanes prepared by using like polyorganosiloxane-polyoxyalkylene block copolymers as emulsifiers and containing in the aqueous phases organic salts respectively. Meanwhile, it is disclosed in Japanese Provisional Patent Publication Nos. 216635/1987, 119844/1988, 180237/1989 and 88513/1989 to prepare like water-in-oil type emulsion compositions using like polyorganosiloxane-polyoxyalkylene block copolymers in combination with other surfactants, gelling agents, etc. Of the block copolymers employed in Examples of these official gazettes, those having polyoxyalkylene chains at each terminal end and as side chains all have polyorganosiloxane chains with polymerization degrees in the range of 64 to 162. However, none of these emulsion compositions have sufficient stability to temperature cycles.
Meanwhile, it is disclosed in Japanese Provisional Patent Publication Nos. 203466/1989 and 93136/1993 to effect emulsification of polyorganosiloxanes using as emulsifiers block copolymers each having a polyoxyalkylene chain at one terminal end of the polyorganosiloxane chain having 50 or less or 150 or less silicon atoms to provide water-in-oil type emulsion compositions having excellent stability to dilution. However, those emulsions obtained using such emulsifiers still do not have sufficient stability to temperature cycles.
Further, it is disclosed in Japanese Provisional Patent Publication Nos. 24959/1979, 268831/1996, and 268832/1996 to use polyorganosiloxane-polyoxyalkylene block copolymers including those of high-molecular weight region as emulsifiers to prepare water-in-oil type emulsion compositions of polyorganosiloxanes. Of the block copolymers employed in examples of these official gazettes, those of the type having polyoxyalkylene chains at each terminal end and as side chains have high polyorganosiloxane chain polymerization degrees of 1.011, and none of emulsion compositions of these block copolymers are successful in satisfying both stability as emulsions per se and stability to temperature cycles.
As a result of out studies, such block copolymers having polyorganosiloxane chains of low polymerization degrees generally provide emulsion compositions having poor stability to temperature cycles, whereas those having polyorganosiloxane chains of high polymerization degrees exhibit poor effects as emulsifiers, and the resulting emulsion compositions per se come to have poor stability.
An objective of the present invention is to provide water-in-oil type emulsion compositions of polyorganosiloxanes which are stable as emulsions per se and show excellent stability to temperature changes particularly to those including cooling to low-temperature regions of xe2x88x925xc2x0 C. or lower and which cause no oil phase and/or aqueous phase separation. Another objective of the present invention is to provide a water-in-oil type emulsion composition which has excellent stability to the temperature changes as described above and is incorporated with components necessary for cosmetics and the like such as salts.
We made studies with a view to attaining the above objectives to find that the intended objectives can be attained by using as an emulsifier a block copolymer having a molecular structure within a specific range where polyoxyalkylene chains are present at each terminal end and as side chains of a polyorganosiloxane chain having a polymerization degree within a specific range and accomplished the present invention.
To describe more specifically, the water-in-oil type emulsion composition according to the present invention is characterized in that it contains:
(A) at least one sort of polyorganosiloxane;
(B) at least one sort of polyorganosiloxane-polyoxyalkylene block copolymer represented by the general formula (I): 
wherein R1s each represent a methyl group and some of R1s may be phenyl groups; Es each represent a group of the general formula (II): 
wherein R2 represents a hydrogen atom, an acyl group or an alkyl group having 1 to 4 carbon atoms; p is an integer of 3 to 6; a is an integer of 2 to 50; b is an integer of 0 to 50; and a+b is an integer of 5 to 100; m is an integer of 300 to 600; n is an integer of 1 to 30; and m+n is an integer of 300 to 600; and
(C) water.
The component (A) employed in the emulsion composition of the present invention is a polyorgano-siloxane constituting the oil phase as a continuous phase and includes silicone fluids ranging from those of low-viscosity values to high-viscosity values and gumlike siloxane high polymers which may be linear or contain small amounts of branched siloxane structures. The component (A) also includes linear or cyclic siloxane oligomers, trimethylsiloxysilicic acid and cyclic compounds thereof. The organic groups bonded to the silicon atoms include linear or branched alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl, tetradecyl, hexadecyl and octadecyl; cycloalkyl groups such as cyclohexyl; aralkyl groups such as 2-phenylethyl and 2-phenylpropyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl and tolyl; and substituted monovalent hydrocarbon groups such as 3,3,3-trifluoropropyl, 3-aminopropyl and 3-(2-aminoethyl)-aminopropyl, and the organic groups may be of one or more sorts.
The silicone fluids and gumlike siloxane high polymers can be exemplified by polydimethylsiloxane, polymethylphenylsiloxane, polymethylvinylsiloxane, polymethyl(higher alkyl)-siloxane, polymethyl(3,3,3-trifluoropropyl)siloxane, polymethyl(3-aminopropyl)-siloxane and polymethyl[3-(2-aminoethyl)aminopropyl]-siloxane; whereas the siloxane oligomers can be exemplified by octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane. These silicone fluids and gumlike siloxane high polymers may be used alone or as a combination of two or more sorts, for example, a mixed siloxane prepared by dissolving a gumlike siloxane high polymer in a cyclic siloxane. Further, they may be used in the form of solution in hydrocarbon solvents such as n-hexane and xylene.
When the resulting emulsion compositions are used as cosmetics, silicone fluids such as polydimethylsiloxane, polymethylphenylsiloxane, polymethyl(3-aminopropyl)-siloxane and polymethyl[3-(2-aminoethyl)aminopropyl]-siloxane; gumlike siloxane high polymers such as polydimethylsiloxane; and cyclic siloxane oligomers such as octamethylcyclotetrasiloxane and decamethylcyclopentacyloxane are preferred among others.
While the content of the component (A) in the silicone emulsion composition may not particularly be limited, it is usually 5 to 90% by weight, preferably 10 to 80% by weight, and more preferably 15 to 60% by weight.
The polyorganosiloxane-polyoxyalkylene block copolymer of the component (B) employed in the emulsion composition of the present invention is an emulsifier for effecting emulsification of the oil-phase polyorgano-siloxane, the aqueous-phase water and other components added as necessary to form a water-in-oil type emulsion composition. What is characteristic to the present invention is that a water-in-oil type silicone emulsion composition which is stable to temperature cycles including cooling to low temperature regions of xe2x88x925xc2x0 C. or lower can be obtained by using a polyorganosiloxane-polyoxyalkylene block copolymer within a specific range to be described below as the emulsifier.
The component (B) described above is represented by the general formula (I): 
wherein R1, E, m and n have the same meanings as defined above, respectively.
It should be noted here that in the general formula (I), m and n merely represent the numbers of the two sorts of inner siloxane units, respectively, and these two sorts of inner units are arranged at random. R1s each represent a methyl group, and some of R1s (e.g., up to 40 mol %) may be phenyl groups.
m representing the number of the inner diorgano-siloxane units containing no E is an integer of 300 to 600. n representing the number of the inner siloxane units in which E is bonded to the silicon atom is an integer of 1 to 30, preferably 3 to 15. However, the polymerization degree of the units m+n, i.e. the polysiloxane chain excluding the both terminal end units, is 300 to 600. If the polymerization degree of the units m+n is less than 300, the resulting emulsion composition shows poor stability to temperature cycles including low-temperature regions; whereas if it exceeds 600, the resulting emulsion per se comes to have poor stability.
E is a group containing a polyoxyalkylene chain. What is characteristic to the component (B) employed in the present invention is that E is present at each terminal end of the polysiloxane and as side chains in some of the inner units thereof. E is represented by the general formula (II): 
wherein R2, p, a and b have the same meanings as defined above, respectively.
In the general formula (II), a and b merely represent the number of oxyethylene units and that of the oxypropylene units in E, respectively. While these two sorts of units are usually arranged at random in the E chain, they may be arranged blockwise, for example, in the form of block-copolymized chain such that the oxyalkylene moiety consisting of the oxypropylene units may be located on the siloxane side.
p is an integer of 3 to 6 so as to obtain excellent chemical stability between the silicon atoms and the polyoxyalkylene chains, particularly preferably 3 so as to facilitate synthesis and handling. a is an integer of 2 to 50, preferably 5 to 30; and b is an integer of 0 to 50, preferably 0 to 20. That is, the polyoxyalkylene moiety of E is either a polyoxyethylene chain or an oxyethylene-oxypropylene copolymer chain, with the proviso that a+b is an integer of 5 to 100, preferably 10 to 80. If a and b are not within the specified ranges, the composition of the present invention comes to have poor stability.
R2 is the terminal group of E and is exemplified by a hydrogen atom; an acyl group such as acetyl; and an alkyl group such as methyl, ethyl, propyl and butyl.
While the component (B) may be in the form of liquid, semi-solid or solid at ambient temperature, it is preferably liquid at 25xc2x0 C. in view of ease of handling.
The component (B) can be exemplified by those represented by the following formulae (III) to (VI): 
It should be noted that in the above and the following formulae, two sorts of inner siloxane units in the polyorganosiloxane chain and two sorts of oxyalkylene units in the polyoxyalkylene chain are arranged at random, respectively.
The component (B) can be synthesized as follows. For example, there is synthesized a polyorganohydrogensiloxane having a hydrogen atom bonded to a silicon atom in each terminal group to which E is to be incorporated and in some of the inner units. A polyoxyalkylene having at one terminal end R2 and at the other end an alkenyl group such as an allyl group is added to the polyorganohydrogen-siloxane and the resulting mixture is heated in the presence of a platinum catalyst to bring about an addition reaction between the Sixe2x80x94H bond in the polyorganohydrogen-siloxane and the alkenyl group of the polyoxyalkylene, and thus the polyoxyalkylene is introduced into the poly-organosiloxane to synthesize a block copolymer as the component (B). The platinum catalyst can be exemplified chloroplatinic acid, a platinum complex obtained by heating chloroplatinic acid and an alcohol, a platinum-olefin complex and a platinum-vinylsiloxane complex.
While the content of the component (B) in the silicone emulsion composition may not particularly be limited, it is preferably 0.1 to 30% by weight, more preferably 0.5 to 10% by weight.
In the present invention, the component (C) is water and constitutes the aqueous phase as a dispersed phase in the emulsion composition of the present invention. While the content of the component (C) in the silicone emulsion composition may not particularly be limited, it is preferably 5 to 80% by weight, more preferably 10 to 50% by weight.
The salt to be added optionally to the emulsion composition of the present invention may not particularly be limited so long as it does not impair stability of the emulsion to temperature changes, which is the feature of the present invention, and is exemplified by aluminum salts such as aluminum chloride, aluminum chlorohydrate and aluminum citrate; aluminum-zirconium double salts such as aluminum-zirconium tetrachlorohydrate and aluminum-zirconium tetrachlorohydrate-glycine complex; zinc salts such as zinc chloride, zinc sulfate, zinc undecylenoate, zinc palmitate, zinc stearate and zinc p-phenolsulfonate; and salts of amino acids such as glycine, alanine, valine, leucine, isoleucine, serine, aspartic acid and glutamic acid.
The content of the salts to be added to the emulsion composition is usually up to 50% by weight, and those salts which are known as astringent agents including, for example, aluminum salts, aluminum-zirconium double salts and zinc salts are preferably added in an amount of 5 to 30% by weight in view of their effects, stability, particularly excellent stability to temperature changes, of the resulting emulsion.
The emulsion compositions of the present invention can be incorporated with polyhydric alcohols such as propylene glycol, 1,3-butylene glycol, glycerol, sorbitol and polyethylene glycol, and addition of such polyhydric alcohols is preferred since they can improve moisturizing effects of the resulting emulsion compositions when they are employed as cosmetics.
Further, the emulsion composition of the present invention may be incorporated with a surfactant other than the component (B), an antioxidant, an antiseptic, a antifungi agent, a humectant, a UV absorber, a lower alcohol, a perfume, an extender pigment, a color pigment, etc., so long as the effect of the present invention is not impaired.
The emulsion composition of the present invention can be prepared by premixing the components (A), (B) and (c), and other components which are added optionally and then emulsifying the resulting mixture using conventional emulsifying means such as a homomixer and a homogenizer.